How to calculate gas mileage
MPG = miles driven ÷ gallons used
Fill the tank, reset the trip meter (or note the odometer). Drive normally for at least half a tank, then refill. Divide miles driven by gallons to refill = your MPG. For accuracy, average over several tanks.
Example
- Trip distance: 280 miles
- Gallons to refill: 10
- MPG: 280 ÷ 10 = 28 MPG
- Cost per mile at $4.478/gal (EIA's U.S. regular average, week of September 21, 2026): $4.478 ÷ 28 = $0.160/mile
The word under your result (Excellent 35+, Good 25–34.9, Average 20–24.9, Below Average 15–19.9, Poor under 15) is this site's rule of thumb for a passenger car, not an official grade. The EPA measures each model's fuel economy and publishes it at fueleconomy.gov; it does not rank cars this way.
Example MPG by vehicle type
Rough ranges to show the spread between vehicle types. They are illustrations, not EPA figures: your model's rating is on its window sticker and at fueleconomy.gov.
| Vehicle type | Example MPG |
|---|---|
| EV (MPGe) | 100–130 MPGe |
| Plug-in hybrid (PHEV) | 50–100 MPGe |
| Hybrid (Prius, RAV4) | 40–55 MPG |
| Compact (Civic, Corolla) | 30–35 MPG |
| Sedan (Camry, Accord) | 25–32 MPG |
| Small SUV (CR-V, RAV4) | 25–30 MPG |
| Mid-size SUV | 20–25 MPG |
| Large SUV / 3-row | 17–22 MPG |
| Pickup truck (F-150, Silverado) | 18–22 MPG |
| Heavy-duty truck | 12–18 MPG |
| Sports car | 15–22 MPG |
For comparison, the EPA puts the average gasoline vehicle on the road at about 22.2 MPG, driven around 11,500 miles a year (EPA, Greenhouse Gas Emissions from a Typical Passenger Vehicle).
Tips to improve gas mileage
- Check tire pressure monthly, under-inflated tires lower gas mileage by about 0.2% for every 1 psi drop in average pressure (fueleconomy.gov). The right pressure is on the driver's door jamb sticker.
- Keep highway speeds moderate, air resistance climbs steeply as you go faster, so fuel use per mile rises with speed.
- Don't idle, an idling engine burns fuel for zero miles. Switch off when you are parked and waiting.
- Remove excess weight, the engine has to move everything you carry. Clean out the trunk.
- Remove roof racks when not in use, a cargo box on top adds drag, most of all at highway speeds.
- Use cruise control on flat highways, maintains steady speed, improving efficiency.
- Accelerate smoothly, hard starts and late braking waste fuel. Coast to red lights.
- Combine errands, cold starts use extra fuel. One longer trip is more efficient than many short ones.
- Keep up with maintenance, use the recommended grade of motor oil and fix faults such as a failing oxygen sensor. On a modern fuel-injected car a clogged air filter hurts acceleration but not MPG (fueleconomy.gov).
MPG vs liters per 100km
The US and UK use miles per gallon; most other countries use liters per 100 km (lower is better). They're inverses:
L/100km = 235.21 ÷ MPG
The constant comes from 1 mile = 1.609344 km and 1 US gallon = 3.785411784 L (NIST). Quick reference: 25 MPG = 9.4 L/100km, 30 MPG = 7.8 L/100km, 40 MPG = 5.9 L/100km, 50 MPG = 4.7 L/100km. Note: UK gallons are 20% larger than US gallons (4.55L vs 3.79L), so 30 UK MPG = 25 US MPG.
Cost per mile at this week's gas prices
Regular gasoline for the week of September 21, 2026, from the EIA's Gasoline and Diesel Fuel Update: the U.S. average and the cheapest and dearest of its regions that week.
| MPG | Gulf Coast (PADD 3) $3.972 | U.S. average $4.478 | West Coast (PADD 5) $5.600 |
|---|---|---|---|
| 15 MPG | $0.265 | $0.299 | $0.373 |
| 20 MPG | $0.199 | $0.224 | $0.280 |
| 25 MPG | $0.159 | $0.179 | $0.224 |
| 30 MPG | $0.132 | $0.149 | $0.187 |
| 35 MPG | $0.113 | $0.128 | $0.160 |
| 40 MPG | $0.099 | $0.112 | $0.140 |
| 50 MPG | $0.079 | $0.090 | $0.112 |
Annual fuel cost comparison (11,500 miles, $4.478/gal)
| Vehicle type | MPG | Annual cost |
|---|---|---|
| Heavy-duty truck (example) | 15 | $3,433 |
| Large SUV (example) | 19 | $2,710 |
| Pickup truck (example) | 20 | $2,575 |
| EPA: average car on the road | 22.2 | $2,320 |
| Sedan (example) | 28 | $1,839 |
| Compact car (example) | 32 | $1,609 |
| Hybrid (example) | 45 | $1,144 |
Miles and the 22.2 MPG row are the EPA's typical passenger vehicle; the price is EIA's U.S. regular average for the week of September 21, 2026. The other MPG values are examples. Electric and plug-in vehicles are left out because their running cost depends on your electricity price, not the gas price.
Frequently asked questions
How do I calculate my car's gas mileage?
Fill the tank, note the odometer reading (or reset the trip meter). Drive until the tank is half empty or lower, then fill up again. MPG = miles driven ÷ gallons used to refill. Example: drove 280 miles, used 10 gallons to refill = 28 MPG. For accuracy, calculate over several tanks. Many modern cars show real-time and average MPG in the dashboard display.
What is good gas mileage?
No agency grades it. The EPA tests each model and prints the result on the window sticker and at fueleconomy.gov, and it puts the average gasoline vehicle on the road at about 22.2 miles per gallon (EPA, Greenhouse Gas Emissions from a Typical Passenger Vehicle). Beating that figure means you burn less than the typical car around you. The Excellent-to-Poor word this calculator shows is its own rough scale for passenger cars, so pickups and big SUVs will usually sit lower on it.
How much does it cost to drive 100 miles?
Take 100, divide by your MPG, then multiply by what you pay per gallon. Using EIA's U.S. average for regular in the week of September 21, 2026 ($4.478 a gallon): 25 MPG comes to $17.91, 30 MPG to $14.93, 20 MPG to $22.39 and 15 MPG to $29.85. Prices move every week and differ by region, so put your own pump price into the calculator.
How do I calculate fuel cost for a trip?
Fuel cost = (trip distance ÷ MPG) × gas price per gallon. For a 500-mile trip at 28 MPG, paying $4.478 (EIA's U.S. regular average for the week of September 21, 2026): 500 ÷ 28 = 17.86 gal, times the price = $79.96. For round trips, double the distance or tick the round-trip box.
Does AC use more gas?
Yes. The compressor is driven by the engine, so running it costs fuel, and the effect is largest on hot days and short trips. Driving with the windows down adds aerodynamic drag instead, which matters more at highway speed than around town. Which of the two costs more depends on the car and how fast you are going.
Why is my gas mileage getting worse?
Common causes: (1) under-inflated tires, which fueleconomy.gov says cost about 0.2% of gas mileage for every 1 psi drop in average pressure; (2) the wrong grade of motor oil, worth 1%–2% by the same source; (3) a failing oxygen sensor or other engine fault; (4) dragging brakes; (5) many short trips and cold starts; (6) hard acceleration and braking; (7) extra weight or a roof box. A clogged air filter on a modern fuel-injected car hurts acceleration but, per fueleconomy.gov, not MPG. Check tire pressure monthly and follow the maintenance schedule.
What is the difference between MPG and MPGe?
MPG is miles per gallon of gasoline, a direct efficiency measure for gas vehicles. MPGe (miles per gallon equivalent) is how the EPA rates electric and other alternative-fuel vehicles: it converts the energy the vehicle uses into the amount of gasoline holding the same energy, so the two can be compared on efficiency. MPGe says nothing about cost; what an EV costs to run depends on your electricity price per kWh.
How many gallons does it take to drive 500 miles?
Divide 500 by your MPG. At 25 MPG: 20.0 gallons. At 28 MPG: 17.9 gallons. At 32 MPG: 15.6 gallons. At 35 MPG: 14.3 gallons. At $4.478 a gallon (EIA, week of September 21, 2026), 25 MPG costs $89.56 and 35 MPG costs $63.97, a gap of $25.59 per 500 miles.
Does driving speed affect gas mileage?
Yes. Air resistance grows quickly with speed, so a car uses more fuel per mile at 75 mph than at 55 mph. Stop-and-go traffic hurts too, because each start spends fuel to get the car moving again. Holding a steady, moderate speed with cruise control on open road is the simplest way to use less.
How do I convert MPG to liters per 100km?
Divide 235.21 by the MPG figure (it comes from 1 mile = 1.609344 km and 1 US gallon = 3.785 L). So a car doing 25 MPG burns 9.4 litres per 100 km, 35 MPG is 6.7, and 50 MPG is 4.7. The two scales run in opposite directions: more MPG means fewer litres. An imperial (UK) gallon is bigger than a US gallon, so UK MPG figures look higher for the same car.